We will continue our investigation of estrogen induced Leydig cell carcinogenesis in the mouse looking particularly at the effects of early Leydig cell proliferation and hyperprolactinemia upon tumor development. The cytosol estrogen binding and estrogen translocation into the nucleus will be investigated in normal Leydig cells and in neoplastic Leydig cells with special reference to the responsiveness of the later to hormonal manipulation. The phenomenon of estrogen induced regression of transplantable Leydig cell tumors is also under investigation. The possible deleterious effect of the maternal ingestion of estrogens upon offspring is being investigated in mice with emphasis upon fecundity, developmental abnormalities, and subsequent tumor development.